1. Field of the Invention
This invention relates in general to the art of shearing continuously running web material such as paper, and is more particularly concerned with rotary slitter apparatus wherein cooperating slitter elements often refer to as a slitter and a slitter band slit the web as the web travels longitudinally through the slitter.
2. Description of Prior Art
Slitters of the kind with which the present invention is concerned are well represented in U.S. Pat. Nos. 3,122,958; 3,459,086 3,682,023, the disclosures of which to any extent necessary are incorporated herein by reference, and in particular as to advantageous orientations of the cooperating rotary slitter members. A major problem that these patents have addressed has been the attainment of clean severance with minimum dust generation and clean non-frayed edges on the slit web. In addition, these patents present various schemes for improving the wearing qualities of the cooperating slitting edges of the rotating slitter elements.
However, there is still room for improvement in the cutting edges of the rotary slitter element. When it is considered that the slitters operate at web running speeds of up to 6,000 feet per minute it will be appreciated that the wear factor is of considerable concern. In U.S. Pat. No. 3,122,958 it was proposed to prolong slitter life by applying a bonded thin layer of spark-deposited carbide surface on the perimeter or axial face of the rotary slitter elements, together with beveling of the slitter member back of the applied hard layer and running out to the edge of the layer to afford support for the cutting edge of the slitter member.
In U.S. Pat. No. 3,459,086, it is indicated that a thin hardened layer of wear resisting material such as tungsten carbide or aluminum oxide applied as by flame coating process may be used, similarly as in U.S. Pat. No. 3,122,958. In addition, a suggestion is made that the outer layer may be in the form of a separate band which is shrink-fitted in place, with a machining or grinding of the outer surface to obtain concentricity. However, this U.S. Pat. No. 3,459,086 indicates the necessity of providing complete underlying support for the hardened peripheral layer, and much attention is given to the effects of wear on the cutting action of the band and blade.
In U.S. Pat. No. 3,682,032 the problem is attacked by provision of lips formed on the body of the blade, with a hardened layer on the perimeter over the lip and coextensive with the axial dimension of the lip.